1. Field of the Invention
This invention relates to a novel photorecording element which utilizes a change in the orientation of liquid crystal by light, to a method for the production of the photorecording element, and to a liquid crystal cell comprising the same photorecording element. More particularly, this invention relates to a photorecording element which is produced by forming on a liquid crystal by adsorption a thin film of a macromolecular compound possessing a residue capable of undergoing a reversible change of structure under the influence of light, the element being able to change the orientation of its liquid crystal layer upon irradiation with light, and to temporarily or permanently record information by utilizing the change in the orientation of the liquid crystal layer, to a method for the production of the photorecording element, and to a liquid crystal cell comprising the photorecording element.
2. Prior Art Statement
As recording elements using a liquid crystal, those which rely for storage of information upon electrical principles and those which rely for storage of information on optical principles are known to the art. Those of the former kind are chiefly used for display devices, and of those of the latter kind have been applied to photorecording.
The information stored by a liquid crystal display which displays information using electrical principles is lost when its power supply is cut off and, therefore, such displays require a special device to ensure permanent preservation of information. Further, since such displays inevitably uses patterned electrodes, they have an insufficient resolving power and prove to be unsuitable as photorecording elements of high capacity.
The liquid crystal photorecording elements which utilize optical principles include those of the type which utilize the heat generated by a laser beam or the like for causing a change in the phase of liquid crystal. Though the photorecording elements of this type are applicable to high-density photosensitive recording, their applications are limited because the recording is attained solely in the form of pits. The photorecording elements of the type which incorporate therein a compound capable of photochemically changing the structure and attain a change in the phase by the action of light upon the compound exhibit an outstanding resolving power during the early stage of the storage of input information. Because of the fluidity of liquid crystal, however, they are liable to suffer from a marked loss of resolving power with elapse of time. For example, the photochromic cholesteric liquid crystal which is obtained by dissolving azobenzene, a chiral compound, in nematic liquid crystal is transformed by the action of ultraviolet light into an isotropic phase and is enabled to record information by virtue of this transformation of phase. However, it has a disadvantage in that the liquid crystal eventually begins to flow and the recorded image begins to loss sharpness (Glossary of Lectures for the 52nd Spring Meeting of Japan Chemical Society, 1986).
An invention perfected by inventors including Kunihiro Ichimura, Takahiro Seki, and Takashi Tamaki who are found among the inventors of the invention of the subject patent application has be en already filed for a U.S. patent application under Ser. No. 07/238,398, to which a Notice of Allowance dated May 8, 1990 has been issued. The invention of this U.S. patent application consists of the following elements:
(a) Transparent substrate, PA0 (b) Photochromic compound disposed in direct contact with said transparent substrate and capable of reversibly changing its structure on exposure to light, and PA0 (c) Liquid crystal. PA0 (1) A photorecording element consisting essentially of (a) a transparent substrate, (b) a layer of a macromolecular compound capable of undergoing a reversible change in structure upon exposure to light, deposited by adsorption on the substrate, and (c) a layer of liquid crystal deposited directly on the layer of the macromolecular compound. PA0 (2) A method for the production of the photorecording element mentioned above, which essentially consists in applying on a transparent substrate a mixture of a liquid crystal substance with a macromolecular compound capable of undergoing a reversible change in structure upon exposure to light and allowing the applied layer of the mixture to stand at rest. PA0 (3) A method for the production of the aforementioned photorecording element, which essentially consists in applying on a transparent substrate a macromolecular compound capable of undergoing a reversible change in structure upon exposure to light and applying further thereon a liquid crystal substance. PA0 (4) A liquid crystal cell, comprising a liquid crystal layer, layers of a macromolecular compound capable of undergoing a reversible change in structure upon exposure to light, one each superposed on the opposite surfaces of the liquid crystal layer, and substrates one each superposed on the outer surfaces of the layers of the macromolecular compound, providing that the layers of the macromolecular compound are deposited fast by adsorption on the substrates and at least one of the two substrates is transparent.
This earlier invention was intended to eliminate drawbacks suffered by the known elements described above. To be specific, it is directed to providing a photorecording element which utilizes a change in orientation of a liquid crystal caused by a light and which suffers no degradation of resolving power with elapse of time owing to the flowability of the liquid crystal.
For this element to be rendered practicable, however, it requires further improvement in quality.